An in vitro system of cultured aortic endothelial cells will be used to study tumor-endothelial cell interactions. We will focus on more fundamental studies of the synthesis and ultrastructure of the endothelial cell matrix and the effect of matrix on tumor cell behavior, because we believe that to fully understand tumor-endothelial cell interactions we must first understand matrix-endothelial cell and matrix-tumor cell interaction, respectively. To accomplish these goals we propose the following: 1) studies on the effects of tumor cells on endothelial cell migration over isolated matrix and purified matrix components; 2) studies on the incorporation of exogenous matrix components into the matrix; 3) construction of defined matrices using purified matrix components.